#!/bin/bash
#Copyright 2002 William Stearns <wstearns@pobox.com>
#Released under the GPL.
Version='0.3'

if [ "$1" = "-h" ]; then
	echo "hostlookup version $Version" >>/dev/stderr
	echo "  Returns the hostnames of IP addresses given on command line or stdin." >>/dev/stderr
	echo "Usage" >>/dev/stderr
	echo "  hostlookup 127.0.0.1	Hostname for this address" >>/dev/stderr
	echo "  hostlookup 127.0.0.	Scan this class C" >>/dev/stderr
	echo "  hostlookup 127.0.	Scan this class B" >>/dev/stderr
	echo "  echo 12.13.14.15 12.13.14.16 | hostlookup" >>/dev/stderr
	
	exit 1
fi


CommandLine='no'

dolookup () {
	SPLITIP=$1
	I1O1=${SPLITIP%%.*} ; SPLITIP=${SPLITIP#*.}
	I1O2=${SPLITIP%%.*} ; SPLITIP=${SPLITIP#*.}
	I1O3=${SPLITIP%%.*} ; SPLITIP=${SPLITIP#*.}
	I1O4=$SPLITIP

	if [ -n "$I1O1" -a -n "$I1O2" -a -n "$I1O3" -a -n "$I1O4" ]; then
		#All 4 octets, single IP check
		( host -t PTR "$I1O1.$I1O2.$I1O3.$I1O4" 2>/dev/null || echo 'domain name pointer ' ) | grep 'domain name pointer' | sed -e 's/.*domain name pointer //' | sed -e "s/^/$I1O1.$I1O2.$I1O3.$I1O4	/"
	elif [ -n "$I1O1" -a -n "$I1O2" -a -n "$I1O3" ]; then
		#3 octets, class C loop
		echo "Scanning class C $I1O1.$I1O2.$I1O3." >>/dev/stderr
		for Octet4 in `seq 0 255` ; do
			( host -t PTR "$I1O1.$I1O2.$I1O3.$Octet4" 2>/dev/null || echo 'domain name pointer ' ) | grep 'domain name pointer' | sed -e 's/.*domain name pointer //' | sed -e "s/^/$I1O1.$I1O2.$I1O3.$Octet4	/"
		done
	elif [ -n "$I1O1" -a -n "$I1O2" ]; then
		#2 octets, class B loop
		echo "Scanning class B $I1O1.$I1O2." >>/dev/stderr
		for Octet3 in `seq 0 255` ; do
			for Octet4 in `seq 0 255` ; do
				( host -t PTR "$I1O1.$I1O2.$Octet3.$Octet4" 2>/dev/null || echo 'domain name pointer ' ) | grep 'domain name pointer' | sed -e 's/.*domain name pointer //' | sed -e "s/^/$I1O1.$I1O2.$Octet3.$Octet4	/"
			done
		done
	elif [ -n "$I1O1" ]; then
		echo Won\'t scan a class A.
	fi
}



while [ -n "$1" ]; do
	dolookup "$1"
	CommandLine='yes'
	shift
done


if [ "$CommandLine" = 'no' ]; then
	while read IPS ; do
		set $IPS
		while [ -n "$1" ]; do
			dolookup "$1"
			shift
		done
	done
fi